A writing instrument such as described in German patent documents 2,319,942 of G. Edel and 2,456,905 of N. Otake et al has an elongated hollow barrel having a front end formed with a longitudinally extending tip passage centered on and defining an axis and provided internally with an ink reservoir. A rigid synthetic-resin tip extending along the axis and formed with longitudinal capillaries has a front pointed end which projects axially forwardly from the barrel and a rear end which is in the reservoir. The tip projects axially forwardly from the barrel so that ink in the reservoir can be drawn through the tip's capillaries to its front end and there transferred to a writing surface.
In order to retain the tip in place the barrel may be formed as described in the above-cited Otake reference with a bump projecting radially inward into the passage so as to engage the tip and retain it in a force fit. Such a formation does not hold the tip solidly enough, so that a strong rearwardly directed blow to the tip can actually drive it backward into the barrel. The above-cited Edel reference proposes forming the tip asymmetrically with a radially outwardly open groove that is of increasing depth toward one end of the tip. Radially inwardly projecting ribs in the passage engage in this groove, providing a fairly good hold. Nonetheless in this arrangement the use of an asymmetrical tip makes manufacturing the pen somewhat more complex in that a separate device must be provided to properly orient the tips before they are inserted into the barrels. Similarly U.S. Pat. No. 3,969,027 of G. Randar proposes another asymmetrical tip having a radially outwardly open groove that snap fits with a radially inwardly projecting collar in the front end of the passage. Once again, the asymmetry of the tip complicates assembly of the pen, and fabrication of the tip is made more complex by the necessity of making it of smaller diameter rearward of the groove.